Archaebacteria are a special group of bacteria that can survive in extremely harsh environmental conditions where most other organisms cannot live. They are found in habitats such as very hot springs, highly salty lakes, acidic environments and marshy areas lacking oxygen. These organisms have unique cell wall structures and metabolic pathways that help them tolerate extreme temperature, salinity and acidity. Because of their ability to live in such extreme habitats, archaebacteria are often called extremophiles and are considered very important in studying early life on Earth.
2. Archaebacteria that live in extremely salty areas are called:
Correct Answer: B
Halophiles are archaebacteria that live in environments with very high salt concentration. These organisms are commonly found in salt lakes, salt pans and other saline environments where most organisms cannot survive. The word 'halo' means salt and 'phile' means loving, indicating that these organisms thrive in salty conditions. Their cellular machinery and enzymes are specially adapted to function properly even in high salt concentrations, which would normally damage most other living cells.
3. Archaebacteria that live in hot springs are known as:
Correct Answer: C
Thermoacidophiles are archaebacteria that live in extremely hot and acidic environments such as hot springs and volcanic areas. The word 'thermo' means heat and 'acidophile' means acid-loving. These organisms are able to survive at very high temperatures and low pH levels where most organisms would die. Their enzymes and cellular components are specially adapted to remain stable and functional under such extreme conditions, making them important for studying biochemical processes in extreme environments.
4. Archaebacteria that live in marshy areas and produce methane are called:
Correct Answer: B
Methanogens are archaebacteria that live in anaerobic environments such as marshy areas, swamps, sewage and the digestive systems of ruminant animals like cows and buffaloes. They produce methane gas as a by-product of their metabolic activities. Because these organisms generate methane, they play an important role in the carbon cycle. Methanogens are also responsible for producing biogas in biogas plants and are important in ecological processes involving decomposition of organic matter.
5. Archaebacteria are able to survive in extreme conditions mainly because of their:
Correct Answer: A
Archaebacteria differ from other bacteria mainly in the structure of their cell wall. Their cell wall does not contain the typical peptidoglycan found in most bacteria. Instead, they have unique chemical compositions that make the cell wall more stable and resistant to extreme environmental conditions. Because of this special structure, archaebacteria can survive in harsh habitats such as very salty environments, hot springs, highly acidic areas and marshy regions where most other organisms cannot live.
6. ___________ are present in the gut of several ruminant animals such as cows and buffaloes and produce methane (biogas) from dung.
Correct Answer: B
Methanogens are a type of archaebacteria that live in anaerobic environments such as marshy areas and the digestive systems of ruminant animals like cows and buffaloes. These microorganisms help break down organic matter and produce methane gas as a metabolic by-product. This methane forms the main component of biogas produced from animal dung in biogas plants.
7. Eubacteria are thousands of different bacteria also called as ______.
Correct Answer: A
Eubacteria are commonly known as true bacteria. They represent the typical bacteria found in nature and include thousands of different species. These bacteria are prokaryotic organisms that lack a true nucleus and membrane-bound organelles. They are found in many environments such as soil, water, air and inside living organisms. Eubacteria include both useful and harmful types, such as decomposers, nitrogen-fixing bacteria, and disease-causing bacteria.
8. Eubacteria are characterised by the presence of a ______ and if motile, a ______.
Correct Answer: A
Eubacteria, also called true bacteria, typically have a rigid cell wall that provides structural support and protection. Many eubacteria are motile, meaning they can move from one place to another. Their movement is usually carried out by a flagellum, a long whip-like structure that rotates and helps the bacterium swim in liquid environments. Not all bacteria possess flagella, but when present, this structure plays an important role in bacterial movement, helping them reach favorable environments or nutrients.
9. Cyanobacteria are:
Correct Answer: A
Cyanobacteria are autotrophs because they can prepare their own food through photosynthesis. They contain the pigment chlorophyll a, similar to green plants, which allows them to capture sunlight and convert carbon dioxide and water into organic food. Because of this ability, cyanobacteria are called photosynthetic autotrophs and they play an important role as primary producers in many aquatic ecosystems.
10. Cyanobacteria are also referred to as:
Correct Answer: A
Cyanobacteria are commonly known as blue-green algae. They are photosynthetic prokaryotic organisms that contain pigments similar to those found in plants, allowing them to perform photosynthesis. Even though they are called algae, cyanobacteria are actually bacteria because they lack a true nucleus and other membrane-bound organelles. They are widely found in aquatic environments such as ponds, lakes, and oceans, as well as in moist soils. Cyanobacteria play an important role in nature by producing oxygen and contributing to nitrogen fixation in some ecosystems.
11. Cyanobacteria have ______ similar to green plants.
Correct Answer: A
Cyanobacteria contain the photosynthetic pigment chlorophyll a, which is also present in green plants. This pigment enables them to perform photosynthesis and produce their own food using sunlight, carbon dioxide and water. Because of this ability, cyanobacteria play an important role as primary producers in aquatic ecosystems. In addition to chlorophyll a, they also possess other pigments such as phycocyanin, which gives them their characteristic blue-green colour.
12. The cyanobacteria are ______ autotrophs.
Correct Answer: A
Cyanobacteria are photosynthetic autotrophs. They contain the pigment chlorophyll a, which allows them to capture sunlight and carry out photosynthesis. Using light energy, they convert carbon dioxide and water into organic food molecules. This process is similar to the way green plants produce food. Cyanobacteria are commonly found in aquatic environments such as ponds, lakes and oceans, and they play an important role in ecosystems by producing oxygen and acting as primary producers in food chains.
13. Cyanobacteria may occur as:
Correct Answer: C
Cyanobacteria show different structural forms in nature. They may occur as single cells (unicellular), as groups of cells living together (colonial), or as long thread-like chains of cells (filamentous). This structural diversity allows them to adapt to many aquatic and moist environments such as ponds, lakes, rivers and damp soils.
14. Cyanobacteria are commonly known as:
Correct Answer: A
Cyanobacteria are commonly called blue-green algae and occur widely in nature. They are found in freshwater, marine environments and also on land in moist places such as soil, rocks and tree bark. Because they can live in aquatic as well as terrestrial habitats and perform photosynthesis like algae, they are often referred to as freshwater, marine or terrestrial algae.
15. In cyanobacteria, the colonies are generally surrounded by a:
Correct Answer: A
Cyanobacteria may occur as unicellular, colonial or filamentous forms and are commonly found in freshwater, marine and terrestrial habitats. In many species, the cells form colonies that are embedded within a gelatinous sheath. This gelatinous covering helps protect the cells from environmental stress such as drying, harmful chemicals or predators. It also helps the colony remain together as a group. Because of this sheath, cyanobacterial colonies often appear as slimy or jelly-like masses on moist surfaces or in water bodies.
16. Cyanobacteria often form ______ in polluted water bodies.
Correct Answer: A
Cyanobacteria are photosynthetic microorganisms that may occur as unicellular, colonial or filamentous forms. They are commonly found in freshwater, marine and terrestrial habitats. In polluted water bodies rich in nutrients such as nitrogen and phosphorus, cyanobacteria multiply rapidly and form dense populations called blooms. These blooms often appear as greenish or bluish layers on the surface of water. Such algal blooms can reduce oxygen levels in water and may harm aquatic organisms, affecting the balance of the ecosystem.
17. Some cyanobacteria fix atmospheric nitrogen in specialised cells called:
Correct Answer: A
Certain cyanobacteria are capable of fixing atmospheric nitrogen and converting it into usable forms like ammonia. This process occurs in specialised thick-walled cells called heterocysts. Heterocysts provide an anaerobic environment required for nitrogen fixation because the enzyme nitrogenase cannot function in the presence of oxygen. Cyanobacteria such as Nostoc and Anabaena possess heterocysts and play an important role in increasing soil fertility by adding nitrogen to the environment.
18. Examples of cyanobacteria that contain heterocysts for nitrogen fixation are:
Correct Answer: A
Heterocysts are specialised thick-walled cells present in some filamentous cyanobacteria that fix atmospheric nitrogen. These cells create a low-oxygen environment necessary for the nitrogenase enzyme to function. Nostoc and Anabaena are common examples of cyanobacteria that contain heterocysts and play an important role in enriching soil with nitrogen, especially in aquatic environments and rice fields.
19. Chemosynthetic autotrophic bacteria oxidise inorganic substances such as ______ to obtain energy for ATP production.
Correct Answer: A
Chemosynthetic autotrophic bacteria obtain energy by oxidising inorganic substances instead of using sunlight. These substances include nitrates, nitrites and ammonia. During this process, chemical energy is released, which is used to produce ATP. The energy stored in ATP is then used to synthesise organic compounds from carbon dioxide. This process is called chemosynthesis. Such bacteria play an important role in nutrient cycles, especially the nitrogen cycle, by converting nitrogen compounds into forms that can be used by plants and other organisms.
20. Chemosynthetic autotrophic bacteria play an important role in recycling nutrients such as:
Correct Answer: A
Chemosynthetic autotrophic bacteria obtain energy by oxidising inorganic substances like nitrates, nitrites and ammonia. The energy released from these chemical reactions is used for ATP production and for synthesising organic compounds. These bacteria play a very important role in biogeochemical cycles by recycling essential nutrients in nature. They convert compounds of nitrogen, phosphorus, iron and sulphur into usable forms that can be absorbed by plants and other organisms. Because of this activity, chemosynthetic bacteria help maintain the balance of nutrients in ecosystems and support the productivity of soil and aquatic environments.
21. Heterotrophic bacteria are most abundant in nature and most of them act as:
Correct Answer: B
Heterotrophic bacteria are the most abundant type of bacteria found in nature. They cannot produce their own food and depend on organic matter for nutrition. Many of these bacteria act as decomposers, meaning they break down dead plants, animals and other organic materials into simpler substances. During this process, nutrients are released back into the soil and environment, which can then be reused by plants and other organisms. Because of this important role in recycling nutrients and maintaining ecosystem balance, heterotrophic bacteria are essential for the functioning of natural ecosystems.
22. Many heterotrophic bacteria are beneficial to humans because they help in:
Correct Answer: A
Many heterotrophic bacteria play an important role in human life and agriculture. Some bacteria help convert milk into curd through the process of fermentation. Certain bacteria are used in the production of antibiotics that help treat diseases. Others, such as Rhizobium, live in the root nodules of leguminous plants and fix atmospheric nitrogen into forms usable by plants. Because of these beneficial activities, bacteria are widely used in food production, medicine and agriculture.
23. The bacteria that converts milk into curd is called:
Correct Answer: B
Lactobacillus is the bacterium responsible for converting milk into curd. It is a lactic acid bacterium that ferments lactose (milk sugar) present in milk into lactic acid. The lactic acid causes the milk proteins to coagulate, resulting in the formation of curd. Lactobacillus is widely used in the dairy industry for preparing curd, yogurt and other fermented milk products. These bacteria are also considered beneficial because they help improve digestion and maintain a healthy balance of microorganisms in the human gut.
24. Which bacterium is commonly used in the production of antibiotics?
Correct Answer: C
Streptomyces is a group of bacteria well known for producing many important antibiotics used in medicine. These bacteria live mainly in soil and belong to the group actinomycetes. They produce several widely used antibiotics such as streptomycin, tetracycline and chloramphenicol. Antibiotics produced by Streptomyces help kill or inhibit the growth of harmful disease-causing microorganisms. Because of this ability, Streptomyces bacteria play a very important role in pharmaceutical industries and medical treatments.
25. Which bacterium fixes atmospheric nitrogen in the root nodules of leguminous plants?
Correct Answer: B
Rhizobium is a nitrogen-fixing bacterium that lives symbiotically in the root nodules of leguminous plants such as peas, beans and groundnut. These bacteria convert atmospheric nitrogen into ammonia or other usable nitrogen compounds that plants can absorb and use for growth. In return, the plant provides food and shelter to the bacteria. This symbiotic relationship is very important in agriculture because it naturally enriches the soil with nitrogen, reducing the need for chemical fertilizers.
26. Some bacteria that cause diseases in humans, crops and animals are called:
Correct Answer: B
Some bacteria are harmful and cause diseases in humans, plants and animals. Such disease-causing microorganisms are called pathogens. Pathogenic bacteria can infect human beings and cause diseases such as cholera, tuberculosis and typhoid. They can also infect crops and reduce agricultural productivity, as well as affect farm animals and pets. Because of their harmful effects, pathogenic bacteria are studied carefully in medical and agricultural science so that methods can be developed to control infections and protect human health, livestock and crop production.
27. Cholera in humans is caused by which bacterium?
Correct Answer: A
Cholera is a serious water-borne disease caused by the bacterium Vibrio cholerae. This bacterium infects the small intestine and produces toxins that lead to severe diarrhoea and dehydration. Cholera spreads mainly through contaminated water or food. Proper sanitation, clean drinking water and good hygiene practices are essential for preventing this disease. Vibrio cholerae is a comma-shaped bacterium belonging to the group Vibrio.
28. Typhoid fever is caused by which bacterium?
Correct Answer: B
Typhoid fever is caused by the bacterium Salmonella typhi. This bacterium infects humans through contaminated food and water. The disease is characterised by high fever, weakness, abdominal pain and loss of appetite. Poor sanitation and unsafe drinking water are common causes of typhoid outbreaks. Vaccination, proper hygiene and clean water supplies are important measures for controlling the spread of this disease.
29. Tetanus is caused by which bacterium?
Correct Answer: C
Tetanus is caused by the bacterium Clostridium tetani. This bacterium is commonly found in soil, dust and animal dung. It enters the body through cuts or wounds and produces a toxin that affects the nervous system. The disease causes painful muscle stiffness and spasms. Tetanus can be prevented through proper vaccination and good wound care.
30. Citrus canker in plants is caused by which bacterium?
Correct Answer: B
Citrus canker is a plant disease that affects citrus plants such as oranges, lemons and limes. It is caused by the bacterium Xanthomonas citri. The disease produces raised lesions on leaves, stems and fruits, which can lead to leaf drop and reduced fruit quality. Citrus canker spreads through wind-driven rain, contaminated tools and infected plant material.
31. Bacteria mainly reproduce by:
Correct Answer: B
Bacteria mainly reproduce by a simple asexual method called binary fission. In this process, a single bacterial cell divides into two identical daughter cells. First, the genetic material (DNA) replicates, and then the cell elongates and splits into two equal halves. Each new cell receives a copy of the genetic material. This method allows bacteria to reproduce very rapidly under favorable conditions, leading to large populations in a short time.
32. Under unfavourable conditions, bacteria produce:
Correct Answer: B
Under unfavourable environmental conditions such as lack of nutrients, extreme temperature or dryness, some bacteria form spores. These spores are thick-walled, resistant structures that help bacteria survive harsh conditions. When the environment becomes favourable again, the spores germinate and develop into active bacterial cells. This ability allows bacteria to survive for long periods even in extreme environments.
33. A primitive type of sexual reproduction in bacteria occurs through:
Correct Answer: B
Although bacteria mainly reproduce asexually by binary fission, they can also exchange genetic material through a primitive form of sexual reproduction. In this process, DNA is transferred from one bacterium to another through mechanisms such as conjugation, transformation or transduction. This exchange of genetic material does not produce new cells directly but increases genetic variation among bacterial populations, helping them adapt to changing environmental conditions.
34. Which organisms completely lack a cell wall?
Correct Answer: B
Mycoplasma are unique bacteria that completely lack a cell wall. Because they do not have a rigid cell wall, they can change their shape easily and are called pleomorphic organisms. Mycoplasma are among the smallest living cells capable of independent existence. They possess only a plasma membrane surrounding the cell. Due to the absence of a cell wall, they are resistant to certain antibiotics that target cell wall synthesis, such as penicillin.
35. Which organisms are the smallest living cells known and can survive without oxygen?
Correct Answer: B
Mycoplasma are the smallest known living cells capable of independent existence. They lack a cell wall and are surrounded only by a plasma membrane. Because of their extremely small size and simple structure, they can pass through filters that normally trap bacteria. Many Mycoplasma species are facultative anaerobes, meaning they can survive even in the absence of oxygen. They may live as parasites in plants, animals and humans, sometimes causing diseases.
36. Many Mycoplasma are:
Correct Answer: C
Many species of Mycoplasma are pathogenic and cause diseases in both animals and plants. They are very small bacteria that lack a cell wall and can survive in various environments. In animals and humans, some Mycoplasma species cause respiratory and other infections. In plants, they are responsible for several plant diseases that affect growth and productivity. Because of their parasitic lifestyle, Mycoplasma often depend on host organisms for nutrients.